What is hip dysplasia? The hip, or coxofemoral joint, is a ball-andsocket joint comprising a cup-shaped socket and the head of the thigh bone or femur, which is roughly spherical. These are held in place by soft tissues and, to some extent, the surrounding muscles. The term ‘hip dysplasia’ is used to describe hip joints which are loose and/or ill-fitting, many of which will develop osteoarthritis as the dog ages. In the young puppy, the skeleton is fairly soft and any laxity or incongruity of the hip joint will result in an abnormal conformation. As the animal matures, this abnormality becomes permanent as the skeleton hardens. Even following skeletal maturity (at about one year of age) abnormal stresses on the bones and soft tissues can continue to cause bony remodelling and the production of arthritic new bone. How can hip dysplasia be diagnosed? Certain clinical signs such as pain on rising or abnormal gait can lead to a suspicion of hip dsyplasia but it must be confirmed with an Xray. However, many dogs with hip dysplasia show no clinical signs until later in life, when arthritis has developed. If they have been used for breeding, hip dysplasia genes will have been passed to their offspring. The condition is a disease which is governed partly by genetic features and partly by environmental factors such as nutrition, bodyweight and exercise. Therefore, the radiograph simply records the physical end-result of a variety of causes and, at present, this is the best tool for screening dogs for hip dsyplasia. Although different assessment criteria are used in different countries, discussions between interested parties are ongoing in an attempt to provide some international standardisation. How are hip radiographs taken? Radiographs are taken when the dog is lying on its back with its hind legs extended and rotated inwards so that the thigh bones are parallel. The advantage of this position is that it can be reproduced consistently on different occasions, although a number of other projections may be employed to provide supplementary information. Sedation or general anaesthesia are necessary to allow accurate positioning without the need for the animal to be held. The radiographs must be identified accurately with the dog’s Kennel Club registration number, the date and a right/left marker. What is the Kennel Club Hip Dysplasia Scoring Scheme? In the UK an assessment scheme is run under the joint auspices of the Kennel Club and the British Veterinary Association (BVA). Dogs are radiographed by the owner’s veterinary surgeon and the radiographs are submitted to the BVA where each film is examined by 2 veterinary surgeons from its panel of expert scrutineers. Nine anatomical parameters are examined from each hip joint and allocated a score, ranging from 0 (perfect) to 6 (worst). The scoring scheme allows dogs within a breed to be compared with each other, and dogs should only be used for breeding if their hip score is well below the average score for that breed. It is also helpful to consider the hip scores of the parents, grandparents and siblings when selecting a dog or bitch for breeding. Dogs should only be used for breeding if their hip score is well below the average score for that breed. Ruth Dennis MA VetMB DVR DipECVDI MRCVS R.C.V.S. Recognised Specialist in Radiology European Specialist in Veterinary Diagnosticr.